It is known to integrate heat pumps with domestic hot water heaters wherein the hot gases are used in heat exchange with water circulated from the hot water heater to provide an added heat source to heat water and this usually results in complex devices integrated together in a single unit. A disadvantage of such integrated devices is that because domestic hot water heaters utilize glass-lined casings whose life span is usually short, and when such becomes defective it is necessary to effect expensive modifications or to change the entire integrated device unit instead of only the hot water tank. Also, maintenance of integrated systems can be expensive depending on its structure. Accordingly, there is added fabrication costs and service cost when using integrated hot water systems and this cost can sometimes obviate the projected economical advantages of such systems. Such advantages include lower electrical energy consumption as it is less expensive to operate a compressor of a heat exchanger than the electrical resistive elements of water heaters. However, the refrigeration system provides cool air conditioning.
With gas-fired hot water heaters there is also considerable heat loss to the environment through the exhaust flue. There is also a need to considerably reduce such heat loss.
Because water tanks of domestic water heaters have a relatively short life, it would also be beneficial to heat the water exteriorly of the tank whereby tank replacement would be less costly. Also, the water heater could be serviced independently.